1. Field of the Invention
This invention relates to a process for the preparation of 2-chloro-5-chloromethyl-1,3-thiazole. 2-Chloro-5-chloromethyl-1,3-thiazole prepared according to the present invention is useful as a synthesis intermediate for agricultural chemicals, for example, as a synthesis intermediate for hexahydrotriazine compounds useful as insecticides (refer to Japanese Patent Publication No. HEI 6-776).
2. Discussion of the Background
As a preparation process of 2-chloro-5-chloromethyl-1,3-thiazole, known are (1) a process of reacting allyl isothiocyanate with chlorine (refer to Japanese Patent Application Laid-Open No. SHO 63-83079) and (2) a process of reacting 2-chloroallyl isothiocyanate with a chlorinating agent (refer to Japanese Patent Application Laid-Open No. HEI 4-234864).
The reaction described in the above process (1) is however markedly severe reaction which requires a large excess amount of a chlorinating agent and high temperature and in addition, plural byproducts are formed together with the target product 2-chloro-5-chloromethyl-1,3-thiazole so that this process is accompanied by the problem that 2-chloro-5-chloromethyl-1,3-thiazole so obtained has low purity. On the other hand, the process described in the above (2) is also accompanied with the problem that 2-chloroallyl isothiocyanate, which is a starting material, is not available at low cost. Accordingly, it is difficult to say that each of these processes is an industrially excellent process for the preparation of 2-chloro-5-chloromethyl-1,3-thiazole.
In addition, a process of heating 3-chloro-1-thiocyanato-2-propene in dioxane is known as a process for the preparation of 3-chloro-1-isothiocyanato-1-propene (refer to Journal f. prakt. Chemie. 322(4), 629(1980)).
It is however known that the above process has a low yield (refer to Comparative Example 2 which will be described below) and dioxane which is used as a solvent is carcinogenic. Accordingly, it is difficult to say that this process is industrially advantageous for the preparation of 3-chloro-1-isothiocyanato-1-propene.
Furthermore, as a process for the preparation of 3-chloro-1-thiocyanato-2-propene, a process of reacting 1,3-dichloropropene and potassium thiocyanate in dimethyl sulfoxide is shown (refer to Journal f. prakt. Chemie. 322(4), 629(1980)).
The above process however has a yield as low as 47% so that it is difficult to say that it is an industrially advantageous process for the preparation of 3-chloro-1-thiocyanato-2-propene.
With respect to the processes described in the above (1) and (2), isolation and purification of 2-chloro-5-chloromethyl-1,3-thiazole are carried out by distillation.
Since 2-chloro-5-chloromethyl-1,3-thiazole has low thermal stability and its reflux ratio cannot be increased, 2-chloro-5-chloromethyl-1,3-thiazole purified by distillation has a low purity. It is difficult to say that distillation is an excellent purification method for 2-chloro-5-chloromethyl-1,3-thiazole. Accordingly, there is a demand for a purification method to obtain 2-chloro-5-chloromethyl-1,3-thiazole having a higher purity.